In modern internal combustion engines devices for variably adjusting the timing control of gas exchange valves are used in order to be able to vary the phase relationship between the crankshaft and the camshaft within a defined angular range, between a maximum advanced position and a maximum retarded position. For this purpose the device is integrated into a power train, via which torque is transmitted from the crankshaft to the camshaft. This power train may be embodied as a belt drive, a chain drive or a gear drive, for example.
The device includes at least two rotors turning in opposition to one another, one rotor being drive-connected to the crankshaft and the other rotor being rotationally fixed to the camshaft. The device comprises at least one pressure compartment, which is subdivided by means of a moveable element into two pressure chambers acting in opposition to one another. The moving element is operatively connected to at least one of the rotors. By feeding hydraulic fluid to the pressure chambers or discharging it from the pressure chambers, the moving element is displaced inside the pressure compartment, thereby producing a specific rotation of the rotors relative to one another and, consequently, a rotation of the camshaft relative to the crankshaft.
The flow of hydraulic fluid to and from the pressure chambers is controlled by means of a control unit, generally a hydraulic directional control valve. In turn, the control unit is controlled by means of a regulator, which with the aid of sensors determines the actual and set-point position of the camshaft relative to the crankshaft (phase position) and compares them with one another. When a difference between the two positions is detected, a signal is sent to the control unit, which adjusts the flows of hydraulic fluid to the pressure chambers to this signal.
In order to ensure that the device functions, the pressure in the hydraulic fluid circuit of the internal combustion engine must exceed a specific value. Since the hydraulic fluid is generally supplied by the oil pump of the internal combustion engine and the supplied pressure therefore increases synchronously with the rotational speed of the internal combustion engine, below a certain rotational speed, the oil pressure is still too low to vary or to maintain the phase position of the rotors with any accuracy. This may be the case, for example, during the starting phase of the internal combustion engine or during idle running phases.
During these phases the device would perform uncontrolled oscillations, which leads to increased noise emissions, increased wear, uneven running and increased raw emissions of the internal combustion engine. In order to prevent this, it is possible to provide mechanical locking devices, which, during the critical operating phases of the internal combustion engine, securely couple the two rotors rotationally together, it being possible to cancel this coupling by the admission of hydraulic fluid to the locking device. Here the locking position may be provided in one of the limit positions (maximum advanced position and maximum retarded position) or between the limit positions.
Such a device is disclosed by U.S. Pat. No. 6,684,835 B2, for example. In this embodiment the device is of vane cell construction, an outer rotor being rotatably supported on an inner rotor in the form of a vane wheel. In addition, two rotational angle limiting devices are provided, a first rotational angle limiting device in the locked state allowing an adjustment of the inner rotor in relation to the outer rotor in a range between a maximum retarded position and a defined middle position (locking position). The second rotational angle limiting device in the locked state allows a rotation of the inner rotor in relation to the outer rotor in a range between the middle position and the maximum advanced position. When both rotational angle limiting devices are in the locked state, the phase position of the inner rotor in relation to the outer rotor is limited to the middle position.
Each of the rotational angle limiting devices comprises a spring-actuated locking pin, which is located in a socket of the outer rotor. Each locking pin is subjected by means of a spring to a force acting in the direction of the inner rotor. A slotted link, which is situated opposite the locking pins in certain operating positions of the devices, is formed on the inner rotor. In these operating positions the pins can engage in the slotted link. In so doing, the respective rotational angle limiting device shifts from the unlocked into the locked state. Each of the rotational angle limiting devices can be brought from the locked into the unlocked state by the admission of hydraulic fluid to the slotted link. In this case, the hydraulic fluid forces the locking pins back into their socket, so that the mechanical coupling of the inner rotor to the outer rotor is cancelled.
The hydraulic fluid is admitted to the pressure chambers and the slotted link by means of a control valve, two working connections, which communicate with the pressure chambers, and a control connection, which communicates with the locking groove, among other things, being formed on the control valve. Other such control valves are disclosed by U.S. Pat. No. 6,779,500 B2. These control valves substantially comprise a conventional 4/3-way proportional valve, which guides the hydraulic fluid flows to and from the pressure chambers, and a 2/2-way directional control valve, which controls the hydraulic fluid flows to and from the rotational angle limiting devices, the valve parts being arranged in series. The two valve parts in this case have a common control piston and a common valve housing.
One disadvantage with these embodiments is the large overall space taken up by the control valve, particularly in an axial direction of the valve housing. Another disadvantage is the large number of control structures that have to be formed on the control piston. This leads to increased costs and larger overall dimensions. A further disadvantage is that these control valves are not suited for use as a central valve, which is arranged in a central socket of the inner rotor. For one thing, the control valves have two inlet connections, to which hydraulic fluid has to be delivered via the inner rotor of the device. This increases the complexity and the susceptibility of the device to malfunction. In addition, the device has to be of broad design in an axial direction, in order that all five connections of the valve can be covered by the socket of the inner rotor. This increases the costs of manufacturing the device. It also increases the overall dimensions and the weight.